<?php

/**
 * @file
 * Provides a helper to properly encode HTML-safe JSON prior to PHP 5.3.0.
 */

/**
 * Encodes a PHP variable to HTML-safe JSON for PHP versions below 5.3.0.
 *
 * @see drupal_json_encode()
 */
function drupal_json_encode_helper($var) {
	switch (gettype($var)) {
		case 'boolean':
			return $var ? 'true' : 'false'; // Lowercase necessary!

		case 'integer':
		case 'double':
			return $var;

		case 'resource':
		case 'string':
			// Always use Unicode escape sequences (\u0022) over JSON escape
			// sequences (\") to prevent browsers interpreting these as
			// special characters.
			$replace_pairs = array(
			// ", \ and U+0000 - U+001F must be escaped according to RFC 4627.
			'\\' => '\u005C',
			'"' => '\u0022',
			"\x00" => '\u0000',
			"\x01" => '\u0001',
			"\x02" => '\u0002',
			"\x03" => '\u0003',
			"\x04" => '\u0004',
			"\x05" => '\u0005',
			"\x06" => '\u0006',
			"\x07" => '\u0007',
			"\x08" => '\u0008',
			"\x09" => '\u0009',
			"\x0a" => '\u000A',
			"\x0b" => '\u000B',
			"\x0c" => '\u000C',
			"\x0d" => '\u000D',
			"\x0e" => '\u000E',
			"\x0f" => '\u000F',
			"\x10" => '\u0010',
			"\x11" => '\u0011',
			"\x12" => '\u0012',
			"\x13" => '\u0013',
			"\x14" => '\u0014',
			"\x15" => '\u0015',
			"\x16" => '\u0016',
			"\x17" => '\u0017',
			"\x18" => '\u0018',
			"\x19" => '\u0019',
			"\x1a" => '\u001A',
			"\x1b" => '\u001B',
			"\x1c" => '\u001C',
			"\x1d" => '\u001D',
			"\x1e" => '\u001E',
			"\x1f" => '\u001F',
			// Prevent browsers from interpreting these as as special.
			"'" => '\u0027',
			'<' => '\u003C',
			'>' => '\u003E',
			'&' => '\u0026',
			// Prevent browsers from interpreting the solidus as special and
			// non-compliant JSON parsers from interpreting // as a comment.
			'/' => '\u002F',
			// While these are allowed unescaped according to ECMA-262, section
			// 15.12.2, they cause problems in some JSON parsers.
			"\xe2\x80\xa8" => '\u2028', // U+2028, Line Separator.
			"\xe2\x80\xa9" => '\u2029', // U+2029, Paragraph Separator.
			);

			return '"' . strtr($var, $replace_pairs) . '"';

		case 'array':
			// Arrays in JSON can't be associative. If the array is empty or if it
			// has sequential whole number keys starting with 0, it's not associative
			// so we can go ahead and convert it as an array.
			if (empty($var) || array_keys($var) === range(0, sizeof($var) - 1)) {
				$output = array();
				foreach ($var as $v) {
					$output[] = drupal_json_encode_helper($v);
				}
				return '[ ' . implode(', ', $output) . ' ]';
			}
			// Otherwise, fall through to convert the array as an object.

		case 'object':
			$output = array();
			foreach ($var as $k => $v) {
				$output[] = drupal_json_encode_helper(strval($k)) . ':' . drupal_json_encode_helper($v);
			}
			return '{' . implode(', ', $output) . '}';

		default:
			return 'null';
	}
}
